ABSTRACT
This chapter discusses the direct methods for neutrino mass determinations. Dealing with a three-body decay and a heavy nucleus, the nucleus takes a negligible recoil energy but balances all momenta so the electron and neutrino momenta are not directly correlated and can be treated independently. For a sensitive neutrino mass search, the neutrino energy should be as small as possible; otherwise, relativity will hide any mass effect. On the other hand the decay rate shrinks with the phase space density and hence with the energy squared. In this way a compromise has to be found to use the most efficient way for a neutrino mass search and it is due to relativity that the mass limits by kinematical methods for the remaining two neutrino flavours are orders of magnitude worse. An experimental aspect where a non-vanishing neutrino mass could show up is the search for electromagnetic properties of neutrinos such as electromagnetic moments.
